Messenger spacecraft maps out Mercury

Md.-built vehicle snaps photographs of little-seen planet

LAUREL -- When NASA's tiny Messenger spacecraft emerged from behind the planet Mercury yesterday afternoon, its radio beacon flashed across the solar system, and 107 million miles away, applause broke out in Maryland.

The Maryland-built probe had just skimmed within 124 miles of the planet's surface, programmed to snap hundreds of photographs of a never-before-seen side of the sun's nearest neighbor. It was humanity's first close-up look at Mercury in almost 33 years.

"Messenger is spectacular," said Alan Stern, NASA's associate administrator for science, who was in the control room near Laurel for the historic flyby. "This is really an historic day for planetary exploration. They're imaging the largest single piece of unexplored real estate in the inner solar system."

Scientists in the mission operations center at the Johns Hopkins University's Applied Physics Lab will see the first photos sometime this afternoon, after Messenger begins transmitting them back to Earth. A public release is expected tomorrow.

Messenger's cameras were expected to capture about half of the 55 percent of Mercury's surface missed by NASA's Mariner 10 spacecraft during three flybys in the 1970s. The craft will capture the rest on a second flyby, in October.

"We have to see the whole planet," said Sean Solomon, the Messenger mission's principle investigator.

He recalled when, in 1959, the first photos of the far side of the moon proved that terrain was far different than the side facing Earth. Their first notions of Mars changed, too, once the whole sphere was photographed.

Messenger is to fly past Mercury twice more before entering orbit the planet in 2011.